1. Field of the Invention
The present invention relates to a target detection system. The target detection system according to this invention is mounted on an automotive vehicle, for example, and is used to aid the driver in driving the vehicle by detecting a preceding vehicle running ahead of his vehicle or an obstacle lying ahead or the like target located ahead of the vehicle driven by the driver.
2. Description of the Related Art
A conventional target detection system uses a fusion algorithm in which the reliability of data is studied by use of the result of detecting a target using a EHF radar and the result of detecting a target by image processing thereby to achieve the optimal result. Such a target detection system comprises an EHF radar, a left camera, a right camera and an image processing ECU (electronic control unit). The ECU includes an image processing microcomputer and a fusion processing microcomputer.
In the processing method using the EHF radar, a specified area ahead is scanned by the extremely high-frequency wave. The strength of the signal power output from the EHF radar and the range are so related to each other that the signal power strength is high for the portion where a target exists and low for the portion where a target does not exist. The EHF radar can measure a far distance with high accuracy but is low in accuracy for the measurement of a near target. Also, the EHF radar outputs a near flag upon detection of a near target.
The image processing microcomputer extracts the edge of each of the two images acquired by the two cameras. The edge positions of the two images are different due to the parallax error between the left and right cameras, and this difference is used to calculate the distance to the target. Image processing can be used to measure the distance over a wide range but is low in accuracy for detection of a far target.
The distance measurement by image processing further has the following problems.
1. (Erroneous recognition) In view of the fact that the edge extraction processing is for simply extracting the edges from an image, the edges of letters written on the road surface, shadows or other objects not three-dimensional and different from the target may be extracted erroneously due to the density difference thereof. In such a case, edges are output in spite of the absence of a target.
2. (Erroneous distance measurement) In the case where an edge is detected by the edge extraction processing, the distance is measured by pattern matching between the images acquired by the two cameras. In this processing, the result may become erroneous in the case where a similar pattern happens to exist.
FIG. 1 shows detection areas defined for the target detection system.
An area 2 in which a target can be detected by image processing has a large range, while an area 3 where a target can be detected by an EHF radar reaches a far distance. In an area 4 where a target can be detected by using both the image processing and the EHF radar, on the other hand, a target can be recognized very reliably by the fusion processing between the output data of the radar and the output data of the image processing. The area 4 is called the fusion area. The microcomputer for fusion processing determines the presence or absence of a target based on an overall decision on both the result of detection by the EHF radar and the result of detection by the image processing microcomputer, and thus recognizes the presence of a target such as a preceding vehicle and calculates the distance, etc.
In the conventional target detection system, the processing time for the fusion algorithm in the fusion processing microcomputer is required in addition to the processing time for the EHF radar and the processing time for the image processing microcomputer, and therefore the total processing time is long. Also, the conventional target detection system has yet to overcome the disadvantages of both the EHF radar, and image processing, sufficiently.